The present invention relates generally to the field of structural pier devices which function as footings or structural supports for walls, platforms, towers, bridges, building foundations and the like, and more specifically to the improved construction of a helical anchor or pier utilized for such purposes.
The foundations of many structures, including residential homes, commercial buildings, bridges, and the like, have heretofore conventionally been constructed of concrete slabs, caissons and footings upon which the foundations walls rest. These footings, which are typically constructed of poured concrete, may or may not be in contact with a stable load-bearing underground soil structure, and the stability of the foundation walls, and ultimately the entire structure being supported, depends on the stability of the underlying soil against which the footings bear.
Oftentimes the stability of the soil, particularly near ground surface, can be unpredictable. Changing conditions over time can dramatically affect the stability of the underlying soil, thereby causing a foundation to move or settle. Such settling can cause cracking and other serious damage to the foundation walls, resulting in undesirable shifting of the supported structure, and consequent damage to windows, doors and the like. This ultimately affects the value of the building and property upon which the building is situated.
In some situations, it has been found that the soil may simply be too unstable to cost effectively utilize concrete footings as the foundation for new construction. In other situations, existing concrete foundation walls have settled, causing damage and requiring repair. In still other situations, such as in some foreign markets, the shortage of concrete and abundance of residential and commercial construction has limited the use of poured concrete footings altogether. All of the above has led to the development and advent of the screw-in helical anchor, which is the subject of the present invention.
The use of such screw-in helical anchors have become increasingly common for use as footings or underpinnings in new building construction, as well as for use in the repair of settled and damaged footings and foundations of existing buildings and other structures. Typically, in new construction, a plurality of such helical anchors are strategically positioned and hydraulically screwed into the ground to a desired depth where the underground stratum is sufficiently stable to support the desired structure. Once in place, the anchors are tied together and all interconnected by settling them within reinforced concrete. In a similar manner, such helical anchors are often positioned along portions of settling and damaged foundation walls of a structure, and utilized to repair the structure by lifting and supporting the settling foundation.
Exemplary systems utilizing Helical anchors or underpinnings of this type are disclosed in U.S. Pat. Nos. 5,011,336, 5,120,163, 5,139,368, 5,171,107, 5,213,448, 5,482,407, 5,575,593, and 6,659,692. The helical anchors in these systems will typically include at least one helical plate or flight welded to a drive shaft or column. The shaft and helical flights are generally constructed of a non-corrosive material, such as galvanized steel, to prevent deterioration of the anchor over time. Typically, the steel utilized will be a commercially available grade of about 0.18% carbon by weight, with a yield and tensile strength in the range of about 40,000-55,000 psi.
By way of example, and depending on the application, a standard round shaft starter section may consist of a round hollow hot or cold rolled welded steel tubular shaft 2-⅞″ thru 7.0″ O.D. typical, with one or more steel helical flights or plates of 6″-14″ in diameter welded at spaced intervals thereto. The helical flights typically range in diameter with the smaller diameter flight nearer the bottom of the drive shaft to ensure that the load-bearing surface of each helix partially contacts undisturbed soil upon insertion into the ground. The pitch of the steel flights may range from 3″-6″, and the starter section will have a pointed lower tip, such as by cutting the tip at a 45 degree angle.
Depending upon the application and depth required for reaching bedrock or other suitably stable strata to support the intended structure, multiple extension shafts also formed of hot or cold rolled steel, which may or may not include additional helical flighting, may be coupled to the starter shaft and each other, as needed. Heretofore, such coupling has been accomplished with the use of separate tubular coupling inserts having an outer diameter slightly smaller than the inside diameter of the extension and starter sections. Others have swelled one end of a shaft so as to form a female coupling for receiving an adjoining shaft. Such couplings are pre-drilled with multiple bolt holes that align with corresponding bolt holes in the adjoining ends of the starter and extension shafts. Bolts received through the aligned openings of the shafts and couplings act to secure the adjoining sections together.
Helical anchors of this type are generally torque-driven to bedrock, or to equal load-bearing strata which attains the installing torque that correlates to the required load-bearing capacity. As required load-bearing capacities increase, so does shaft and flight diameters, depth of installation, and consequently the required torque to install the anchors. As a consequence, it has been found that the greater torque generated at increased depths of installation causes coupling failures between the adjoining shaft sections. At or near the coupling joints, the pre-drilled holes in the shafts and inserts begin to tear laterally under excessive applied drive torque, thereby loosening and weakening the bolted joints, and ultimately causing catastrophic failure many feet below ground level. This is particularly true where the walls of the shafts are swelled and consequently thinned to form coupling ends. In other instances, excessive torque will lead to failure of the welded seams of the tubular shafts themselves, which also begin to split, thus causing further failure and weakening of the anchoring system. While the aforementioned conventional coupling system is adequate in applications requiring light to medium load-bearing capacities, it has proven to be insufficient for applications requiring increased load-bearing capacities and installation torque.
In addition to the above, the conventional coupling method utilizing coupling inserts is cumbersome to employ in that it includes multiple components, and is labor intensive and costly to implement. To couple adjoining drive shafts, a coupling insert must first be inserted within one shaft and bolted thereto utilizing a minimum of two (2) bolts. Then the adjoining shaft must be properly positioned over the remainder of the coupling insert and bolted thereto with a minimum of two (2) bolts. At each joint, a minimum of four (4) bolts are necessary to couple adjoining drive shafts together (2 for each shaft).
It is therefore evident that there is a distinct need for an improved means of coupling the drive shafts of helical anchors so as to withstand the significant forces exerted on such coupling devices in applications requiring increased load-bearing capacities and consequent increased drive torque for installation. It is also evident that the present coupling method is cumbersome, time consuming to implement, and would benefit through simplification. It is with these objects in mind that I have developed an improved helical anchor construction having an integrally-fabricated drive shaft coupling capable of withstanding increased torque under applications requiring significant load-bearing capacity.